1. Field of the Invention
The present invention relates to the production of crystalline alumino-silicates commonly referred to as zeolites or molecular sieves. More specifically, this invention relates to the preparation of faujasite materials having a novel particle size and shape, and to adsorbent and catalyst compositions prepared therefrom.
2. Description of the Prior Art
Crystalline aluminosilicate zeolites, commonly referred to as "molecular sieves," are well known in the art. These materials are characterized by a very highly ordered crystalline structure arranged such that uniformly dimensioned pores result. The crystal structure of these zeolites involves a three-dimensional framework of AlO.sub.4 and SiO.sub.4 tetrahedra which are cross-linked by the sharing of oxygen atoms, so that the ratio of oxygen atoms to the total of aluminum and silicon atoms is equal to two. The electronegativity of these tetrahedra is balanced by the presence within the crystal of cations, usually alkali metal cations, such as sodium and potassium ions.
Faujasite is a naturally occurring alumino-silicate. It has a characteristic X-ray structure. The synthetic materials designated zeolite "X" and zeolite "Y" by the Linde Division of Union Carbide Corporation are commonly referred to as synthetic faujasites. Zeolite Y is described in U.S. Pat. No. 3,130,007 and is generally similar to zeolite X described in U.S. Pat. No. 2,882,244. The chemical formula for zeolite Y given in U.S. Pat. No. 3,130,007 is as follows: EQU 0.9+0.2Na.sub.2 O:Al.sub.2 O.sub.3 :wSiO.sub.2 :xH.sub.2 O
wherein W has a value of greater than 2.5 and up to about 6 and x may have a value as high as 9.
U.S. Pat. No. 3,374,058 to McDaniel et al, U.S. Pat. No. 3,767,771 to Guth, British Pat. No. 1,051,621 to Furtig, and British Pat. No. 1,111,849 to Wolf disclose methods for preparing crystalline aluminosilicate zeolites of the faujasite type wherein various quantities of potassium ions are added to a reaction mixture containing silicate, aluminate, water and sodium hydroxide.
U.S. Pat. No. 3,808,326 to McDaniel discloses a method for preparing zeolites wherein zeolite seeds are added to reaction mixtures which comprise silica, alumina, water and alkali metal hydroxide, such as sodium, potassium, and lithium hydroxides.
The product recovered from the usual methods of preparing synthetic faujasite described in the patent and technical literature is a fine sized, uniformly shaped crystalline zeolite having the well-known equart octahedreal shape disclosed by V. Goldschmidt, Atlas der Krystalloformen, Vol. 8, plate 47, figure 17. Several of the uses for molecular sieves require a product in a size range substantially larger than the size of the product recovered from the preparation processes of the prior art. To meet this demand processes have been developed which add various binders and use forming steps to prepare microspheres, beads, nodules and extrusions containing molecular sieves as the principal ingredient. These products lose some of their effectiveness since the binder is generally inert and acts as a diluent of the molecular sieve activity. Even in the case of the so called "binderless" molecular sieve bodies the transformation of the binder is generally not 100% complete.
The activity of a zeolite composite has to do with the weight of zeolite per unit of volume. Hence a composite with a higher density of zeolite will be more active as well as being stronger. Prior art synthetic faujasite crystallites had certain fixed packing characteristics because of the shape and size of the crystallites produced by prior art processes.
It would be highly desirable to produce synthetic faujasite in a platelet crystallite form which would pack more densely and could be used either alone to form highly active, strong composites or in combination with normally shaped zeolite crystallites as a strong active binder, or lubricant component.